The present invention relates to systems for high pressure lift for turbine start-up and medium pressure hydraulics for turbine operational control. More particularly, the invention relates to a system for supplying hydraulic fluid for both lift and hydraulic systems of a gas turbine.
A Gas Turbine initially at rest must be provided with means to enable the internal xe2x80x98rotorxe2x80x99 to begin its rotation. The rotor initially at rest is supported by xe2x80x98journal bearingsxe2x80x99 located at each end of the rotor. The journal bearing surfaces are void of lubrication film when the rotor is at rest. Thus, the rotor will require sufficient break-away torque to begin its motion. This torque is provided by the turbines xe2x80x98turning gearxe2x80x99 which is comprised of an electric motor linked to the rotor through the use of a speed reduction gearbox. This turning gear in itself will not provide sufficient break-away torque to place the rotor in motion if the rotor was initially stationary and sitting on the journal bearing surface. To lower the required break-away torque and enable the turning gear to place the rotor in motion, the rotor is hydraulically lifted off of the journal bearing surface by turbine lubricating oil (normally 25 psi) which has been xe2x80x98boostedxe2x80x99 to a much higher pressure (over 3000 psi) and then jetted into the bottom of the journal bearing.
This boosted high pressure (over 3000 psi) turbine lubrication oil which is jetted into the bottom of the turbine journal bearing is called xe2x80x98lift oilxe2x80x99. There is a system of valves, pumps, filters, manifolds, and tubing which boosts this lubrication oil to high pressure (over 3000 psi) and then delivers it to the bottom of the turbine journal bearing. This system lifts the rotor off of the journal bearing prior to energizing the turning gear thereby reducing the break-away torque below that provided by the turning gear thus enabling rotation. Since this system lifts the rotor through the use of high pressure hydraulic force provided by the lubrication oil, it is often called a xe2x80x98lift oil systemxe2x80x99.
In order to position various hydraulic actuators required for the gas turbine operation, the gas turbine lubrication oil is boosted to a pressure of 1600 psi. The system of valves, pumps, filters, manifolds, and tubing which boosts this lubrication oil to 1600 psi and then delivers it to various hydraulic actuators is often called the xe2x80x98hydraulic systemxe2x80x99.
Conventionally, both of these systems include complicated manifolds, oil filtration units, and variable volume pumps. Moreover, the standard lift oil system offers no redundancy. Thus, if the pump fails to operate, the gas turbine cannot start up. It has, therefore, been proposed to provide a backup lift oil pump. If a second lift oil pump is provided, however, it must be added to the conventional lift oil system as an option. This leads to significant product variability and the second pump is difficult to install due to limited deckspace availability.
The invention is embodied in a system that uses a single hydraulic pump to provide the fluid, e.g. oil, for the dual functions of high pressure lift for turbine start-up and medium pressure hydraulics for turbine operational control. By providing lift oil and hydraulic oil from a single system, overall system complexity is minimized. Moreover, in the presently preferred embodiments a second hydraulic pump is provided as a back up to both lift and hydraulic requirements for full system redundancy and reliability. This redundant source of lift oil is provided in the presently preferred embodiments without increasing overall system complexity nor required deckspace, as compared to prior systems.
Thus, in accordance with an embodiment of the invention a combined lift and hydraulic fluid supply system for a gas turbine is provided that includes a first pump for receiving hydraulic fluid from a lubricating fluid system and selectively supplying hydraulic fluid at a first pressure sufficiently high for lift system requirements for a gas turbine, a valve for selectively supplying hydraulic fluid to a lift system for a gas turbine, a first fluid flow line for conducting hydraulic fluid from the first pump to the lift system valve, a second flow line in flow communication with the first flow line for receiving at least portion of the fluid pumped by the first pump for supply to the hydraulic system of the gas turbine, and a first pressure regulating valve in the second flow line for reducing the pressure of the fluid flowing therethrough from the first pressure to a lower, second pressure for gas turbine hydraulic system requirements.
In accordance with a preferred embodiment of the invention, the combined lift hydraulic system also has a second pump for selectively receiving hydraulic fluid from the lubricating fluid system and selectively supplying hydraulic fluid at the first pressure, a third fluid flow line for conducting hydraulic fluid from the second pump to the lift system valve, a fourth flow line for receiving at least portion of the fluid pumped by the second pump for supply to the hydraulic system of the gas turbine, and an inlet valve for selectively directing fluid from the lubricating fluid system to at least one of the first and second pumps.
In a preferred embodiment of the invention, furthermore, the first pump, and second pump when provided, is a dual compensated variable volume pump and the system provides for feedback control of the pump(s) in accordance with lift system requirements.
The invention is further embodied in a method for supplying lift and hydraulic fluid for a gas turbine that includes pumping hydraulic fluid with a first pump at a first pressure, sufficiently high for lift system requirements for a gas turbine, through a first flow line; selectively supplying hydraulic fluid at the first pressure from the first flow line to the lift system of a gas turbine through a first valve; directing at least portion of the fluid pumped by the first pump from the first flow line into a second flow line for supply to the hydraulic system of the gas turbine; and reducing the pressure of the fluid flowing through the second flow line from the first pressure to a lower, second pressure for gas turbine hydraulic system requirements.